The Preparation And High-pressure Studies Of Ban₂ Of Metal Diazenides

Metal Diazenides are recently discovered compounds with metal conductive and energetic characters.The preparation,characterization,and high-pressure studies of metal diazenides possess not only abundant scientific content but also significant potential application prospects.At present,the research of mental diazenides is still at its initial stage,and the reaction mechanism,conductive mechanism,and phase transition etc.need to be further studied.In this paper,the metal diazenides of BaN₂ is synthesized by decomposing metal azides of Ba（N₃）₂ under high pressure and high temperature utilizing multi anvil and diamond anvil cell apparatus,based on the high pressure studies on metal azides.Through the high pressure study of the metal diazenides of BaN₂,the high pressure phase transitions of metal diazenides are preliminarily revealed.This provides experimental support for the further systematic exploration of the establishment of a new universal method for the synthesis of mental diazenides and the study of the structure and physical properties of metal diazenides under high pressure.The main achievements are as follows:The metal diazenides of BaN₂ was successfully synthesized by multi-anvil cubic high pressure apparatus,the high-pressure in-situ experimental test of the metal diazenides of BaN₂ was carried out by utilizing the piston-cylinder diamond anvil cell and by means of experimental technology of synchrotron radiation in-situ X-ray diffraction.The structure variation of metal diazenides of BaN₂ under high pressure was analyzed,and multiple high pressure phases were revealed.The specific structural information of one of the high pressure phasesα-BaN₂ was determined.We present the synchrotron radiation in-situ X-ray diffraction studies of metal diazenides of BaN₂ up to 40.36 GPa at room temperature.The experimental results show that the metal diazenides of BaN₂ undergoes the pressure-induced structural phase transition between 13.05 GPa and 14.93 GPa.The phase transition sequence is defined asα-BaN₂→β-BaN₂.During the phase transition ofα-BaN₂ toβ-BaN₂,the symmetry of the crystal unit cell increases,and the diazenides units change from non-parallel to parallel relationship.After being indexed and structural refined by Rietveld method,β-BaN₂ is a tetragonal structure with space group of I4/mmm,and the accurate crystal structure is given.The barium diazene undergoes iso-structural phase transition at 35.90 GPa.The high-pressure phase after iso-structural phase transition is defined asγ-BaN₂.Theγ-BaN₂ is still a tetragonal structure with I4/mmm space group,but the specific crystal structure needs to be confirmed by further work.The bulk modulus ofα-BaN₂ andβ-BaN₂ were fitted by the second and third order Birch-Murnaghan equations,respectively.The fitting results show that the bulk modulus fitted by the second-order and third-order Birch-Murnaghan equations ofα-BaN₂ are 64.49±2.01GPa and 57.86±9.03GPa,respectively.The bulk modulus fitted by the second-order and third-order Birch-Murnaghan equations ofβ-BaN₂ are113.47±1.67GPa and 93.17±16.9GPa,respectively.By comparing the high-pressure of metal diazenides of BaN₂ with the structure of CaN₂ and SrN₂ at ambient pressure,it is considered that the size of alkaline earth metal ions in alkaline earth metal diazenides plays a key role in the crystal structure type.This provides experimental data support for further study of structural confirmation and high pressure phase transition studies of other metal diazenides.